Transmission and drive train for a vehicle

ABSTRACT

A transmission for distributing a drive torque to two drive output shafts, with two planetary gearsets each having at least three shafts. A respective shaft of a planetary gearset is connected to a drive input shaft. Furthermore, one shaft of each planetary gearset constitutes one of the output shafts and in each case at least one further shaft of a planetary gearset is connected with a shaft of another planetary gearset. An operation-status-dependent torque of one shaft can be supported by the connection, depending on an operating status of the other shaft connected thereto, in such manner that when there is a rotation speed difference between the output shafts, a speed-difference-changing torque is applied to the planetary gearsets. Furthermore, a drive train is proposed, in which a drive torque from a drive-power-source is distributed variably in the longitudinal and transverse direction of the vehicle in an operation-status-dependent manner.

This application is a national stage completion of PCT/EP2004/011528filed Oct. 14, 2004 which claims priority from German Application SerialNo. 103 48 960.6 filed Oct. 22, 2003.

FIELD OF THE INVENTION

The invention concerns a transmission for distributing a drive torque toat least two drive output shafts with at least two planetary gearsetseach having at least three shafts and a drive train of a vehicle havinga power source, at least two driven vehicle axles and a transmission.

BACKGROUND OF THE INVENTION

In vehicles known from prior practice, a drive torque produced by apower source or drive engine is transmitted by a transmission device tothe drive wheels of a driven vehicle axle, as necessary. Where vehicles,such as all-wheel passenger cars or all-wheel-drive goods vehicles, aremade with more than one driven axle, the power of the engine in thedrive train of such a vehicle has to be distributed among the drivenvehicle axles.

For this power distribution so-termed differentials are used, which arelocated in the drive train of a vehicle downstream from a main gearboxprovided so that various gear ratios can be engaged. For thelongitudinal distribution of the engine's drive power to several drivenaxles of a vehicle, so-termed longitudinal differentials are used. Inaddition, so-termed transverse differentials or equalizationtransmissions are used for the transverse distribution of the drivepower between two drive wheels of a vehicle axle.

With the help of such distributor transmissions, a drive torque can bedistributed between several driven axles in any desired proportionswithout producing stresses in a drive train. Moreover, the use ofdifferentials enables the drive wheels of a driven vehicle axle to bedriven with different rotation speeds independently of one another inaccordance with the different path lengths of the respective left andright driving tracks, whereby the drive torque can be distributed toboth drive wheels symmetrically and thus without any yaw torque.

However, these two advantages are offset by the drawback that because ofthe equalizing action of a differential, the propulsive forces that canbe transferred to the road by two drive wheels of a vehicle axle or fromtwo or more driving axles is determined in each case by the lower orlowest transferable drive torque of the two drive wheels or drivingaxles. This means that when, for example, a drive wheel resting onsmooth ice skids, no torque higher than that of the skidding drive wheelcan be supplied to the other drive wheel, even when the latter is onground that it could grip. In such a driving situation, the vehiclemight disadvantageously not be able to start off because of theequalizing action of a differential, which allows a difference of speedbetween two drive output shafts of the differential.

Accordingly in practice, it has become customary to prevent equalizationmovement of a differential by suitable means in the event of criticaldriving situations. This is done, for example, by a differential lock,known as such, which can be actuated manually or automatically bymechanical, magnetic, pneumatic or hydraulic means and which fullyprevents any equalization movement by blocking the differential.

Furthermore, automatically lacking differentials, also known asequalizing transmissions with limited slip or locking differentials, areused. Such equalizing transmissions make it possible to transfer atorque to a drive wheel of a driven vehicle axle or to a driven vehicleaxle even when the other drive wheel, or if there are several drivenaxles the other driven axles, are skidding because of poor grip on theground. At the same time, however, the advantage of the above-mentionedyaw-torque-free force transmission is lost and the free adaptation ofthe wheel rotation speeds to the path lengths of the two driving tracksof the two wheels of a driving axle is also disadvantageously prevented.

WO 02/09966 A1 discloses a transmission for a four-wheel-drive vehicle,in which an input shaft is connected to a planetary gearset. Here, theplanetary gearset is made as a three-shaft planetary gearset, such thatan annular gear wheel is in active connection with the input shaft, asolar gear wheel with a first drive output shaft, and the planetarycarrier with a planetary gear system and with another drive output shaftof the transmission. The planetary gear system comprises three solargear wheels and three planetary gears each of which meshes with one ofthe solar gear wheels, which are made integrally with one another andhave a common planetary carrier. The planetary carrier of the planetarygear system and one of its solar gear wheels are each in activeconnection with a brake. These brakes are connected to a force supplyand being operated independently of one another and controlled by anelectronic control device. To the electronic control device areconnected a plurality of sensors, whose signals are received by theelectronic control device and converted into corresponding controlsignals for the two clutches. Depending on the control of the twoclutches, the initial speed and the torque transmitted to the front axleand the drive output speed of the planetary gear system and the torquetransmitted to the rear axle are adjusted.

However, this all-wheel distributor system, known from the prior art,has the disadvantage that variable torque distribution can only beeffected to a limited extent and that its design is elaborate. Owing toits elaborate design, the all-wheel distributor system has large overalldimensions so the all-wheel distributor system takes up more structuralspace and has a high inherent weight.

Accordingly, the purpose of the present invention is to provide atransmission of simple design that can be made inexpensively and a drivetrain of a vehicle by way of which a degree of distribution of a drivetorque can be varied, as necessary, between at least two driven vehicleaxles or between two drive wheels of a driven vehicle axle in such amanner that driving operation of a vehicle is ensured even in criticaldriving situations.

SUMMARY OF THE INVENTION

The transmission according to the invention is a system of simple designwith small overall dimensions, which can be made inexpensively and alsotakes up little structural space.

This is achieved by the feature that the two first shafts of theplanetary gearsets, which are connected to a drive input shaft, are alsoconnected to one another at least by a gear wheel mounted on thehousing. The force input to the transmission, which takes place in thedistributor transmission devices known from the prior art by way of aring gear of large diameter, is provided at most at the outer diameterof the two planetary gearsets in the transmission design. In a simplemanner, this reduces the diameter of the transmission, according to theinvention, compared with those of distributor transmissions known fromcurrent practice, without essentially enlarging the external dimensionsof the transmission in the axial direction.

An alternative and also structural-space-optimized transmission,according to the invention, the active connection between the respectivethird shafts of the first and second planetary gearsets is formed by athird planetary gearset, one of the shafts of the third planetarygearset being fixed on the housing. Owing to the arrangement of thethird planetary gearset between the two third shafts of the first andsecond planetary gearsets, a basic distribution of the drive torquebetween the two output shafts of the transmission, which depends on thetransmission ratio of the third planetary gearset, is first produced.This can then be varied, as necessary, and in a manner that depends onthe operating status by various means in a simple way, such as byintroducing a torque into the active connection via one of the shafts ofthe third planetary gearset.

In the transmission of the invention, the drive torque can bedistributed variably between the two drive output shafts by continuousadjustment of the transmission ratio of a continuously variable ratiodevice comprised in the active connection.

This provides the advantageous possibility of distributing a drivetorque from a drive engine between the two output shafts by way ofoperating-status-dependent control and regulation of the transmissionratio of the continuously variable ratio device of the active connectionwith continuously adjustable degrees of distribution between an upperand a lower limit value of a degree of distribution of the drive torquedelivered to the transmission.

With the drive train for a vehicle comprising a power source with atleast two driven vehicle axles and at least one transmission accordingto the invention as described above, which is arranged so as to enablethe distribution, as necessary, and in an operating-status-dependentmanner, of the drive torque from the power source between the drivenvehicle axles in a power path between the power source and the vehicle'saxles and/or in a power path of a vehicle axle for the distribution, asnecessary, and in an operating-status-dependent manner, of the fractionof the drive torque delivered to the axle in the transverse direction ofthe vehicle between two drive wheels of the vehicle's axle. Thepossibility is given, on the one hand, of continuously distributing adrive torque in the longitudinal and/or the transverse direction of thevehicle and, on the other hand, of constructing a vehicle with astructural-space-optimized and inexpensive drive train. In particular,the structural-space-optimized and inexpensive design of the drive trainreduces the overall production cost of a vehicle and leaves morestructural space free in the area of the drive train, where littlestructural space is usually available in vehicles, compared withsolutions known from current practice.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings in which to improve clarity in thedescription of the various example embodiments, the same numbers areused for components having the same structure and function. The Figuresshow:

FIG. 1 is a basic layout scheme of a transmission according to theinvention;

FIG. 2 is a gear layout of a transmission according to the inventionmade as an axle differential in which the active connection between thetwo planetary gearsets comprises spur gear inversion and an electricmotor;

FIG. 3 is a gear layout of a transmission according to the inventiondesigned as a longitudinal distributor differential, whose activeconnection comprises a third planetary gearset and an electric motorbetween the two planetary gearsets;

FIG. 4 is a gear layout of a transmission according to FIG. 3, in whichthe electric motor is coupled to an annular gear of the third planetarygearset;

FIG. 5 is a gear layout of the transmission according to FIG. 2, inwhich the active connection between the first and second planetarygearsets is made with a continuously variable transmission ratio device;

FIG. 6 is a gear layout of the transmission according to the invention,in which the active connection is made with a continuously variabletransmission ratio device and a third planetary gearset;

FIG. 7 is a gear layout of the transmission according to FIG. 6, inwhich a brake is associated with an annular gear of the third planetarygearset;

FIG. 8 is a gear layout of the transmission according to FIGS. 6 and 7,in which an electric motor is associated with a planetary gear wheel ofthe third planetary gearset;

FIG. 9 is a gear layout of the transmission according to FIG. 3, inwhich the third planetary gearset of the active connection can beengaged by way of a claw-type clutch and in which the active connectionis, in addition, made with two brakes;

FIG. 10 is a graphic representation of a relationship between thetransfer capacities of the brakes shown in FIG. 9 and a degree ofdistribution of a drive torque between two drive output shafts of thetransmission according to the invention;

FIG. 11 is a schematic representation of a drive train of an all-wheelvehicle in which a clutch is provided for the longitudinal distributionof a drive torque between two driven vehicle axles and a transmissionmade according to the invention is provided for the transversedistribution of the fraction of the drive torque delivered to a drivenvehicle axle;

FIG. 12 is another example embodiment of a drive train in which atransmission according to the invention is provided for transversedistribution;

FIG. 13 is a third example embodiment of a drive train in which atransmission according to the invention is provided for longitudinaldistribution and a controlled differential lock for transversedistribution;

FIG. 14 is a fourth example embodiment of a drive train in which a drivetorque is distributed longitudinally by a transmission according to theinvention and transversely by an open differential, and

FIG. 15 is a fifth example embodiment of a drive train in which both thelongitudinal and the transverse distribution of a drive torque areeffected by a transmission according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a basic layout of a transmission or transmissiondevice 1 is shown, which can be used as a differential in a power pathof a vehicle's drive train between a power source and the driven vehicleaxles for the longitudinal distribution of a drive torque from the powersource between at least two driven axles, or in a power path of at leastone of the driven vehicle axles for the transverse distribution of afraction of a drive torque delivered to a driven vehicle axle betweentwo drive wheels of that axle.

The transmission 1 is configured with a first planetary gearset 2 and asecond planetary gearset 3 which, depending on the respectiveapplication concerned, can be made as minus, plus, bevel gear orsequential planetary gearsets. In each case, a first shaft 4, 5 of thetwo planetary gearsets 2, 3 is connected to a drive input shaft 6, whichconstitutes a transmission output shaft of a main gearbox (not shown) ofthe drive train. In each case, second shafts 7 or 8 of the two planetarygearsets 2, 3, respectively, constitute drive output shafts of thetransmission 1, which are in active connection either with the drivenvehicle axles or with the drive wheels of one vehicle axle. A thirdshaft 9 of the first planetary gearset 2 and a third shaft 10 of thesecond planetary gearset 3 are connected to one another via an activeconnection 11.

The active connection 11 is designed such that anoperating-status-dependent torque of the third shaft 9 of the firstplanetary gearset 2 or of the third shaft 10 of the second planetarygearset 3, depending on an operating status of the third shaft 10 of theplanetary gearset 3 or of the third shaft 9 of the first planetarygearset 2, can be supported in such manner that if a difference in speedoccurs between the output shafts 6, 7, by virtue of the activeconnection 11 a torque that influences the said speed difference isapplied to the planetary gearsets 2 and 3 or to the respective thirdshafts 9 and 10 thereof.

For this purpose the active connection can be configured in the mannerdescribed in greater detail below alternatively or in combination with aspeed inversion between the two shafts 9 and 10 in active connectionwith one another, a continuously variable transmission ratio device,with a torque source to increase or reduce a torque on at least one ofthe two shafts 9 and 10 in active connection with one another, and/or athird planetary gearset.

FIG. 2 shows a gear layout of a first example embodiment of thetransmission 1, according to the invention, whose basic layout is shownin FIG. 1. A drive torque from the drive shaft 6 is transmitted by afirst spur gear 12 connected thereto to the first shaft 5 of the secondplanetary gearset 3 made as an annular gear. Furthermore, the drivetorque from the drive shaft 6 is transmitted by the first spur gear 12and a second spur gear 13 mounted on the housing to the first shaft 4 ofthe first planetary gearset 2, which is also made as an annular gear.From there on, the drive torque from the drive shaft 6 is transmitted toplanetary gear wheels 14 and 15 engaged with the two annular gears 4 and5, each respectively mounted to rotate on a web 16 or 17 and driving thetwo webs 16 and 17 by virtue of their rolling movement in the annulargears 4 and 5.

The two webs 16 and 17 of the planetary gearsets 2 and 3 are, in turn,connected to the two drive output shafts 7 and 8, so that the drivetorque transmitted via the first and second spur gears 12, 13, the twoannular gears 4 and 5, the planetary gear wheels 14 and 15 and the webs16 and 17, is transferred to the two output shafts 7 and 8.

The connection of the two planetary gearsets 2 and 3 to a crankshaft ofan internal combustion engine, i.e., in the present case to the driveshaft 6, is effected in this case by respective crown gears providedbetween the first spur gear 12 and the annular gear 5 of the secondplanetary gearset 3 and between the second spur gear 13 and the annulargear 4 of the first planetary gearset 2. Accordingly, there is directengagement between the power source and the two planetary gearsets orthe third shafts 9 and 10 of the planetary gearsets 2 and 3, which aremade as solar gears.

In addition, the planetary gear wheels 14 and 15 mesh, respectively,with the solar gears or third shafts 9 and 10 of the planetary gearsets2 and 3, which are respectively connected to a third spur gear 18 and afourth spur gear 19. The two spur gears 18 and 19 of the third shafts 9and 10 of the two planetary gearsets 2 and 3 are connected to a fifthspur gear 20, so that there is a mechanical connection between the solargears 9 and 10 of the planetary gearsets 2 and 3.

This means that the active connection 11, in the example embodiment ofthe transmission 1 according to FIG. 2 shown only schematically in FIG.1, comprises the third spur gear 18, the fourth spur gear 19, the fifthspur gear 20 and a sixth spur gear 21, which is connected to a device 22for applying a torque to one of the shafts 9, 10 in active connectionwith one another. The device 22 for applying a torque or torque source,is coupled via the sixth spur gear 21 to the two solar gears 9 and 10and consists of an electric motor in the present case.

The design of the active connection 11 with the torque source 22 makesit possible, in an operating-status-dependent manner and depending onthe rotation direction of the electric motor, to apply a torque to theactively connected solar gears 9 and 10 such that, for example, if thereis a rotation speed difference of the transmission 1 between the twooutput shafts 7 and 8, an equalizing action of the transmission 1between the two output shafts 7 and 8 is reduced or increased. In otherwords, by way of the torque source 22, a controlled torque increase ortorque reduction can be applied to the two actively connected solargears or third shafts 9 and 10 of the planetary gearsets 2 and 3, forexample, to counteract any oversteering or understeering while drivinground a bend by increasing the speed difference between the drive wheelsof a driven axle effectively and in a simple manner.

Furthermore, the sensitivity of a vehicle to side wind can be improvedby controlled adjustment of a speed difference between the two outputshafts and thus also between two drive wheels on a vehicle axle.

Alternatively, the torque source 22 can also be made as a hydraulicdrive or some other suitable drive machine. Moreover, it is alsoobviously possible to provide one or more ratio steps between the torquesource 22 and the sixth spur gear 21 in order to be able to apply thecontrolled torque increase or reduction, as necessary, to the activeconnection 11 or to the two actively connected third shafts 9 and 10 ofplanetary gearsets 2 and 3. The torque source 22 is controlled,regardless of whether the design has additional ratio steps by a controldevice (not illustrated), which is integrated in a transmission controldevice of the transmission 1 or which can be made as a separate controlunit. The transmission ratios between the individual spur gear pairs ofthe active connection 11 should have the same value.

If the transmission 1 represented in FIG. 2 is used as an axledifferential for distributing the drive torque to two drive wheels of adriven vehicle axle then, when road conditions are unfavorable, this canlead to a situation in which one drive wheel connected with the outputshaft 7 skids on smooth ground while a drive wheel connected with theoutput shaft 8 remains almost motionless because of good grip on theground. In such an operating condition of the transmission 1, there is alarge speed difference between the two output shafts 7 and 8, as aresult of which the two solar gears 19 and 20, which are stationary whenthe speeds of the two output shafts 7 and 8 are equal, now rotate indifferent rotation directions. On account of their inertia, the rotatingmasses of the active connection 11 and also that of the unenergizedtorque source 22 made as an electric motor counteract this speeddifference, particularly at the beginning of the wheel spin, in such amanner that part of the drive torque from the drive shaft 6 istransferred to the output shaft 8 and starting off is made possible.

If it is desired to influence the equalizing action of the transmission1 between the two output shafts 7 and 8 actively in a controlled waythat depends on the driving situation, the design of the activeconnection 11 between the two actively connected solar gears or thirdshafts 9 and 10 of the planetary gearsets 2 and 3 with the torque source22 is particularly suitable because, by way of an electric motor, on theone hand, a driving effect and, on the other side, a braking effect canbe exerted on the speed difference between the two output shafts of thetransmission 1.

In certain operating situations, it is necessary to block the equalizingaction of the transmission 1. On the one hand, this can be done by wayof the electric motor 22, but over a longer period of time that is anenergetically unfavorable solution. For that reason, a lock 23, made asa disk clutch, is arranged between the two third shafts 9 and 10 of theplanetary gearsets 2 and 3, which in the engaged condition produces afixed connection between the two third shafts 9 and 10 of the planetarygearsets 2 and 3 so that the two output shafts 7 and 8 are driven at thesame speed.

In another embodiment not illustrated here, which correspondsessentially to the principle represented in FIG. 2 but is made withoutthe lock between the two solar gears of the two planetary gearsets,instead of the lock, it is advantageously possible to arrange the torquesource or electric motor together with a rotation direction reverserbetween the two solar gears of the two planetary gearsets. For this, theelectric motor is designed as a motor that can be operated in oil andthe transmission, according to the invention, is then a more compactsystem compared with the version according to FIG. 2.

FIG. 3 shows another example embodiment of a gear layout of thetransmission 1 according to the invention. The gear layout of thetransmission 1, shown in FIG. 3, is a longitudinal distributiondifferential in which the active connection 11 between the third shaft 9of the first planetary gearset 2 and the third shaft 10 of the secondplanetary gearset 3 is made with a third planetary gearset 24.

The third shaft or solar gear 10 of the second planetary gearset 3 isconnected with an annular gear 25 of the third planetary gearset 24 andthe third shaft or solar gear 9 of the first planetary gearset 2 iscoupled to a third shaft or a solar gear 26 of the third planetarygearset 24. Several planetary gears roll between the annular gear orfirst shaft 25 of the third planetary gearset 24 and the solar gear 26of the third planetary gearset 24, of which two planetary gears 27A and27B are shown in FIG. 3.

The planetary gear 27A is mounted to rotate on a planetary carrierarranged fixed on the housing or a second shaft 28 of the thirdplanetary gearset 24. The planetary gear 27B is in active connectionwith a torque source 22 made as an electric motor. The mode of action ofthis torque source 22 is basically the same as that of the torque sourcein the transmission, according to FIG. 2, so that reference can be madehere to the description of FIG. 2 in that connection.

When the electric motor 22 is not energized, the drive torque introducedfrom the drive shaft 6 is distributed to the two output shafts 7 and 8in accordance with a basic distribution of the transmission 1. The basicdegree of distribution is determined by the ratio between the number ofteeth on the annular gear 25 and the number of teeth on the solar gear26 of the third planetary gearset 24. Depending on the torque applied bythe electric motor multiplied by a factor consisting of the ratiobetween the number of teeth on the annular gear 4 of the first planetarygearset 2 or the annular gear 5 of the second planetary gearset 3 andthe number of teeth on the solar gear 9 of the first planetary gearset 2or the solar gear 10 of the second planetary gearset 3, this basicdegree of distribution is displaced in the direction of an upper or alower limit value of the degree of distribution.

FIG. 4 shows a gear layout of the transmission 1, which basicallycorresponds to the gear layout represented in FIG. 3. In thetransmission 1, according to FIG. 4, however, the torque source 22 iscoupled to the annular gear or first shaft 25 of the third planetarygearset 24 and the planetary gears 27A, 27B of the third planetarygearset 24 are mounted on the housing side. The example embodiment ofthe transmission, according to the invention shown in FIG. 4, has smalloverall dimensions in the axial direction than the transmission 1 shownin FIG. 3. To enable this, its diameter is larger than that of thesystem in FIG. 3, since the electric motor 22 made as a hollow shaftmotor surrounds the annular gear 25 of the third planetary gearset 24.

Referring to FIG. 5, a gear layout of a transmission 1, according to theinvention, is shown whose principle corresponds to the gear layout shownin FIG. 1. The annular gear 4 of the first planetary gearset 2 and theannular gear 5 of the second planetary gearset 3 are formed integrallyand connected via a bevel gear 29 with a bevel gear 30 on the driveshaft 6.

The active connection 11, between the third shaft 9 of the firstplanetary gearset 2 and the third shaft 10 of the second planetarygearset 3 in this case, comprises spur gears 31 and 32 connected to thesolar gears 9 and 10. Further spur gears 33, 34 and 35 that mesh withthem and a continuously variable transmission ratio device 36 isarranged between the spur gears 33 and 35. This ratio device 36 is inthis case made as a tension means transmission, such as a belt-type CVT(Continuously Variable Transmission). Obviously, the continuouslyvariable ratio device 36 can also be made as a ball variator, a Beiervariator or suchlike.

Integration of the continuously variable ratio device 36 in the activeconnection 11 enables the degree of distribution of the drive torquebetween the two output shafts 7 and 8 of the transmission 1, startingfrom a basic degree of distribution, to be varied between an upper and alower limit value by corresponding adjustment of the transmission ratioof the ratio device 36.

FIGS. 6 to 8 show three gear layouts of further embodiment variation ofthe transmission device, according to the invention, based on the gearlayout represented in FIG. 3. Here, the active connection 11 between thethird shaft 9 of the first planetary gearset 2 and the third shaft 10 ofthe second planetary gearset 3 is made with the third planetary gearset24 with planetary gears 27A and 27B mounted fixed on the housing andwith a continuously variable ratio device 36. In these variantembodiments of the transmission 1, according to the invention, the basicdegree of distribution between the two output shafts 7 and 8 isdetermined by the transmission ratio of the third planetary gearset 24,which can be displaced between an upper and a lower limit value of thedegree of distribution by corresponding adjustment of the transmissionratio of the ratio device 36, as necessary, and in relation to theoperating status.

The transmission gear layout shown in FIG. 7 differs from that shown inFIG. 6 in that the annular gear 25 of the third planetary gearset 24 canbe braked by a brake 37 in this case made as a disk brake. The brake 37also constitutes a torque source by way of an adjustable blockingaction, known from axle differentials of the prior art, and provided inorder to prevent an equalizing effect of such axle differentials, can bemade continuously variable. In advantageous further developments of thetransmission 1, the brake 37 can also be made as a conical brake, a clawbrake, a belt brake or suchlike.

The versions of the torque source described above, i.e., the electricmotor or brake, have the advantage that they can be arranged in thetransmission 1 fixed to the housing. This enables the transmission as awhole to be of a simple design. That is because of the fact that thesupport of the torque source 22, which in the version of thetransmission 1 according to FIG. 8, is made as an electric motor thatengages with the planetary gear 27A of the third planetary gearset 24,can be effected in the transmission 1 without additional design measureswhich enable rotary transfer of force, pressure or current. This meansthat a hydraulic, electromagnetic or other suitable actuator mechanismfor the variable distribution of a drive torque between the two outputshafts 7 and 8 of the transmission 1 is arranged in the transmissionhousing without rotating in the transmission 1.

Referring to FIG. 9, a gear layout of a further embodiment of thetransmission 1, according to the invention, is shown in which the activeconnection 11 has two power paths parallel to one another. A first powerpath is formed with the third planetary gearset 24 which can, in thiscase, be engaged in the force flow of the transmission 1 by way of aclaw clutch 39. The second power paths is found by two brakes 40, 41,associated respectively with the solar gear 9 of the first planetarygearset 2 and the solar gear 10 of the second planetary gearset 3, whichfix the two solar gears 9 and 10 of the planetary gearsets 2 and 3relative to the transmission housing when they are engaged. When thebrakes 40 and 41 are engaged, the equalizing action of the transmission1 is completely suppressed and the two output shafts 7 and 8 run at thesame speed.

When the claw clutch 39 is disengaged, a degree of distribution of thedrive torque between the two drive output shafts 7 and 8 can be variedbetween 0% and 100% by controlling the two brakes 40 and 41 in themanner to be described with reference to FIG. 10. To reduce power lossin each case, one of the brakes 40 or 41 is preferably operated in theengaged condition and the respective other brake 41 or 40 is operatedbetween a completely open and a completely engaged condition.

FIG. 10 shows three very schematic graphs, a first one gb_40 of whichrepresents the variation of a transfer capacity of the first brake 40between a lower limit value W(u) and an upper limit value W(o). Anothergraph gb_41 shows the variation of the transfer capacity of the secondbrake 41, which corresponds with the graph gb_40 of the first clutch 40.A third graph vt is a graphical representation of the degree ofdistribution of the drive torque between the two output shafts 7 and 8as a function of the variations gb_40 and gb_41 of the transfercapacities of the brakes 40 and 41.

At a Point I where the transfer capacity of the first brake 40corresponds to the lower limit value W(u), essentially no torque issupported in a housing 38 of the transmission 1 by the first brake. Atthe same time, the transfer capacity of the second brake 41 is set atthe upper limit value W(o), at which the second brake is fully engaged.In this operating condition of the two brakes 40 and 41, all the drivetorque from a drive engine or the transmission output torque of a maintransmission is delivered to the output shaft 7 connected to the firstplanetary gearset 2.

In the range between Point I and Point II in the diagram of FIG. 10, thetransfer capacity of the second brake 41 undergoes controlled andregulated adjustment in such a manner that the second brake 41 isengaged. At the same time, the transfer capacity of the first brake 40is changed from its lower limiting value W(u) at which it transfers notorque to the housing 38 of the transmission, towards the direction ofthe upper limiting value W(o) of the transfer capacity, at which thefirst brake 40 is also engaged. This means that the transfer capacity ofthe first brake 40 is steadily increased in the range between Point Iand Point II. In consequence, the degree of distribution of the drivetorque between the two output shafts 7 and 8 changes, since as thetransfer capacity of the first brake 40 increases, an increasingfraction of the drive torque is transferred to the output shaft 8connected to the second planetary gearset 3.

In an operating condition of the transmission 1 which corresponds toPoint II of the diagram in FIG. 10, when both brakes 40 and 41 areengaged, there is a defined degree of distribution of the drive torquebetween the two output shafts 7 and 8.

In a range between Point II and Point III in the FIG. 10 diagram, thetransfer capacity of the first brake 40 undergoes regulated andcontrolled adjustment in such a manner that the first brake 40 isengaged. At the same time, starting from the upper transfer capacitylimiting value W(o) at which the second brake 41 is engaged, thetransfer capacity of the second brake 41 is reduced steadily towards thelower limiting value W(u) of the transfer capacity at which the secondbrake 41 essentially supports no torque in the housing 38 of thetransmission 1.

As can be seen in FIG. 10, the variation vt of the degree ofdistribution of the drive torque between the two output shafts 7 and 8increases with progressive reduction of the transfer capacity of thesecond brake 41 up to its maximum value at Point III, where the drivetorque is transferred completely to the output shaft 8 connected to thesecond planetary gearset 3.

The use of the two controllable and related brakes 40 and 41 makes itpossible to distribute the drive torque between the two output shafts 7and 8 as necessary, which continuous variability and in anefficiency-optimized manner. The control and regulation of the twobrakes, in accordance with the invention as described above, improvesefficiency because one of the two brakes 40 or 41 is operated withoutslip, while the other respective brake 41 or 40 is operated with a speeddifference that corresponds to the operating-situation-dependent drivepower distribution in the drive train. This operating strategy minimizesfrictional losses while retaining all the advantages of an all-wheeldrive controlled by frictional shift elements.

In addition, there is the possibility of synchronizing the claw clutch39 by way of the two brakes 40, 41 and incorporating the third planetarygearset 24 in the force flow of the transmission 1 so that there is apreferred basic degree of drive torque distribution between the twooutput shafts 7 and 8, which is available with low losses apart from thefrictional losses occurring in the teeth of the third planetary gearset24.

FIGS. 11 to 15 show schematic representations of a number of embodimentvariations of a drive train 42 of a motor vehicle, in which, for thelongitudinal or transverse distribution of the drive torque in the drivetrain 42, one of the embodiments, described earlier of the transmissiondevice 1 according to the invention, is combined with various otherdevices, represented only in pictograph form, for distributing a drivetorque in the longitudinal direction of a vehicle between two drivenvehicle axles or in the transverse direction of the vehicle between twodrive wheels of a vehicle axle. With the help of the device fordistributing a drive torque in the drive train, it should be possibleespecially in critical driving situations, to produce a suitabledistribution of the drive torque, especially in critical drivingsituations so that propulsive traction is maintained at the driven axlesor drive wheels of a vehicle or so that drive-stabilizing action can betaken, if necessary.

The drive train 42, shown in FIGS. 11 to 15, each have two drivenvehicle axles 43, 44. In the present case, the axle 43 is a front axleand the axle 44 is a rear axle of a vehicle.

Referring to FIG. 11, the drive train 42 comprises a continuouslyadjustable clutch 45 for the longitudinal distribution of a drive torquebetween the two vehicle axles 43 and 44; an open differential 46 ofknown type for transverse distribution at the font axle 43, and atransmission device 1 for transverse distribution at the rear axle 44configured, according to the invention, or an overlap transmission.

The drive train 42 in FIG. 12 differs from the example embodiment of thedrive train 42 in FIG. 11 in that, for the longitudinal distribution ofa drive torque between the front axle 43 and the rear axle 44, thedevice 46 is provided which, when there is a speed difference betweenthe front axle 43 and the rear axle 44, builds up a hydraulic pressureby way of a pump system 46A with which frictional elements of a diskclutch 46B that can be brought into mutual frictional engagement can beacted upon in such a manner that a speed-difference-reducing torque canbe applied to the two respective axles 43 and 44 while, when the speedsare equal, the pressure build-up is virtually zero.

In the drive train 42 of FIG. 13, the longitudinal distribution of thedrive torque between the front axle 43 and the rear axle 44 is effectedby a transmission 1 configured, according to the invention, and thetransverse distribution of the fraction of the drive torque supplied tothe front axle 43 by an open differential 47. The transversedistribution of the fraction of the drive torque supplied to the rearaxle 44 is effected by a controlled differential lock 49 of a knowntype.

Referring to FIG. 14, a drive train 42 is shown in which, for drivingstabilization and free torque distribution between the front and rearaxles, an overlap transmission 1 configured according to the inventionis integrated, which is combined with brake engagement applicable onindividual wheels. The brake engagement is symbolically representedgraphically in FIG. 14 by the arrow indexed 48. For transversedistribution, open differentials are provided in the power trains ofeach of the vehicle axles 43 and 44.

In the drive train represented in FIG. 15, an overlap transmissionconfigured according to the invention is arranged both in thelongitudinal drive train and in the power train of the rear axle 44,this providing the advantageous possibility of continuously varying adegree of distribution of the drive torque between the two vehicle axles43 and 44, as necessary, and depending on the operating situation, anddistributing the fraction of the drive torque delivered to the rear axle44 between the two drive wheels of that axle, again as necessary, anddepending on the operating situation. The fraction of the drive torquedelivered to the front axle 43 is distributed by an open differential.

Clearly, it is open to the judgment of those with knowledge of thesubject to configure the drive train of a vehicle in the longitudinalpower train and in the power trains in the transverse direction of thevehicle of both vehicle axles with a transmission device according tothe invention. This provides the advantageous possibility of adaptingthe drive torque between all the drive wheels of the drive train inaccordance with the driving situation at the time.

REFERENCE NUMERALS

-   1 transmission device, transmission-   2 first planetary gearset-   3 second planetary gearset-   4 first shaft of the first planetary gearset, annular gear-   5 first shaft of the second planetary gearset, annular gear-   6 drive input shaft-   7 second shaft of the first planetary gearset, drive output shaft-   8 second shaft of the second planetary gearset, drive output shaft-   9 third shaft of the first planetary gearset-   10 third shaft of the second planetary gearset-   11 active connection-   12 first spur gear-   13 second spur gear-   14 planetary gear wheels of the first planetary gearset-   15 planetary gear wheels of the second planetary gearset-   16 web of the first planetary gearset-   17 web of the second planetary gearset-   18 third spur gear-   19 fourth spur gear-   20 fifth spur gear-   21 sixth spur gear-   22 torque source-   23 lock-   24 third planetary gearset-   25 first shaft, annular gear of the third planetary gearset-   26 third shaft, solar gear of the third planetary gearset-   27A,B Planetary gears of the third planetary gearset-   28 second shaft, web of the third planetary gearset-   29 bevel gear-   30 bevel gear of the drive shaft-   31-35 spur gear-   36 continuously variable transmission ratio device-   37 brake-   38 housing of the transmission-   39 claw-type clutch-   40 first brake-   41 second brake-   42 drive train-   43 vehicle axle, front axle-   44 vehicle axle, rear axle-   45 controlled clutch-   46 device-   46A pump system-   46B disk clutch-   47 open differential-   48 arrow-   49 controlled differential lock-   vt degree of distribution of the drive torque between the output    shafts-   gb_40 variation of the transfer capacity of the first brake-   gb_41 variation of the transfer capacity of the second brake-   W(u) lower limit value of the transfer capacity of the brakes-   W(o) upper limit value of the transfer capacity of the brakes

1. A transmission (1) for distributing a drive torque to at least firstand second drive output shafts (7, 8) with at least first and secondplanetary gearsets (2, 3) having at least first, second and third shaftssuch that a respective first shaft (4 or 5) of the first and the secondplanetary gearset (2 or 3) is drivingly coupled to a drive input shaft(6) and a respective second shaft of each planetary gearset (2 or 3)constitutes one of the first and the second drive output shafts (7 or8), and the third shaft (9 or 10) of the first planetary gearset (2 or3) is connected to the third shaft (10 or 9) of the second planetarygearset (3 or 2) by a controllable and regulated active connection (11):wherein if a rotation speed difference occurs between the output shafts(7, 8), a first variable speed-difference-changing torque is applied bythe active connection (11) to the third shaft (10 or 9) and a secondvariable speed-difference-changing torque is applied by the activeconnection (11) to the other third shaft (9 or 10) for varying a degreeof distribution of the drive torque, between the first and the secondoutput shafts (7 and 8) between an upper limit and a lower limit valueby an adjustment of a transmission ratio of a continuously variableratio device (36).
 2. A transmission (1) for distributing a drive torqueto at least first and second drive output shafts (7, 8) via at leastfirst and second planetary gearsets (2, 3) each having at least first,second and third shafts, such that the first shaft (4 or 5) of the firstand the second planetary gearset (2 or 3) is connected to a drive inputshaft (6) and the second shaft of each of the first and the secondplanetary gearsets (2 or 3) constitutes one of the first and the seconddrive output shafts (7 or 8), and the third shaft (9 or 10) of the firstplanetary gearset (2 or 3) is connected to the third shaft (10 or 9) ofthe second planetary gearset (3 or 2) by a controllable and regulatedactive connection (11), and an operating-status-dependent torque of oneof the third shafts (9 or 10) is supported as a function of an operatingstatus of the respective other of the third shafts (10 or 9) activelyconnected thereto via the active connection (11) wherein if a rotationspeed difference occurs between the first and the second output shafts(7, 8), a speed-difference-changing torque is applied by the activeconnection (11) at least for a time to the at least first and secondplanetary gearsets (2, 3) such that the active connection (11) is acontinuously variable transmission (36) for varying a degree ofdistribution of the drive torque, between the first and the secondoutput shafts (7 and 8) between an upper limit and a lower limit valueby an adjustment of a transmission ratio of the continuously variabletransmission (36).
 3. A transmission (1) for distributing drive torquefrom a drive input shaft (6), the transmission comprising: acontinuously variable transmission (36) coupled to a first gear (33) anda second gear (35) for controlling transmission of drive to and from thefirst and the second gears (33, 35); a first planetary gearset (2)having a first shaft (4), a second shaft (7) and a third shaft (9); thefirst shaft (4) being drivingly coupled with the drive input shaft (6);the first gear (33) transmitting drive between the third shaft (9) ofthe first planetary gearset (2) and the continuously variabletransmission (36); the second shaft (7) being a transmission outputshaft and being coupled to both the first shaft (4) and the third shaft(9) of the first planetary gearset (2); a second planetary gearset (3)having at least a fourth shaft (5), a fifth shaft (8) and a sixth shaft(10); the fourth shaft (5) being drivingly coupled with the drive inputshaft (6); the second gear (35) transmitting drive between the sixthshaft (10) of the second planetary gearset (3) and the continuouslyvariable transmission (36); the fifth shaft (8) being a transmissionoutput shaft and being coupled to both the fourth shaft (5) and thesixth shaft (10) of the second planetary gearset (3); and the thirdshaft (9) of the first planetary gearset (2) being coupled, via thecontinuously variable transmission (36), with the sixth shaft (10) ofthe second planetary gearset (3) for varying a degree of distribution ofthe drive torque, between the first and the second output shafts (7 and8) between an upper limit and a lower limit value by a adjustment of atransmission ratio of the continuously variable transmission (36) suchthat upon a rotational difference between the second shaft (7) and thefifth shaft (8), a first variable drive is applied by the continuouslyvariable transmission (36), via the first gear (33) to the second shaft(7) and a second variable drive is applied by the active connection (11)via the second gear (35) to the fifth shaft (8).